Replacement of heavy gaseous material

ABSTRACT

The present invention relates to a method for replacing a sterilizing agent in a gaseous form with an inert gaseous material in a package to be aseptically or sterile filled, wherein the inert gaseous material is selected in such a way that it has a temperature at addition which provides a volume, which is smaller than a volume of sterilizing agent to replace at the temperature at which the sterilization takes place.

TECHNICAL FIELD

The present invention relates to a method for replacing heavy gaseous material from substantially closed containers or closed spaces, in particular after an antimicrobial treatment and prior to an aseptic or sterile filling of said container/package.

BACKGROUND OF THE INVENTION

There is an increasing trend toward products that are highly sensitive to microbiological spoilage. These bio-sensitive products include ready-to-drink beverages, such as tea, coffee, and juice-containing (“health-image”) drinks. Even water can be bio-sensitive, particularly if the water is still (i.e., un-carbonated) or has a high content of calcium/magnesium salts, which are the salts often regarded as healthy.

The filling process for highly bio-sensitive products must avoid virtually all traces of microbiological contamination within the finally closed package. For bottles and cans, this is currently achieved by 3 basic methods: hot-filling, post-filling pasteurization and aseptic filling. In the case of hot-filling, the product is heated before filling and the package is filled with hot product, whereby the product temperature is sufficiently elevated so as to secure the sterility of both package and product, until the package is finally sealed. In the case of post-filling pasteurization, the filled, sealed package is heated for a sufficient time to sterilise its content, or to produce an extended shelf life thereof. In the case of aseptic filling, the product, package and filling equipment are separately sterilised, and filling takes place at ambient temperature and in a sterile-maintained environment.

Aseptic filling does not require elevated temperatures, and therefore it is a more suitable process both for the products themselves and for heat-sensitive packages. Subjecting some products to high temperature for the time periods needed by hot-filling and post-filling pasteurization can affect product stability and cause taste deterioration (often giving a “cooked”, “burnt”, or “non-fresh” taste, usually faint but detectable). Additionally, some plastic packages set severe limitations to hot-filling and post-filling pasteurization, because of the material's inherent temperature sensitivity.

Although many of the above advantages of aseptic filling apply to metal cans and glass bottles, they apply particularly to PET bottles, because of their high heat-sensitivity or polymer pouches and carton pouches. For example, PET bottles, suitable for hot handling, are not only expensive, but also cannot accept the high sterilizing temperatures needed by some products (e.g., tea, coffee). However, the PET bottle is a convenient and attractive package, and can boost the marketability of bio-sensitive products. Therefore, lower-cost and more reliable aseptic filling methods can become an important marketing tool for such products. In the present case package denotes any type of package, either rigid or soft.

In further detail, aseptic filling involves filling at ambient temperature, whilst ensuring that the microbiological content of the finally packaged product is sufficiently low to ensure a sterile packaged product Current methods for aseptic filling of beverage packages (cans or bottles) involve maintaining a sterile filling space. The sterile filling space is achieved either by maintaining the entire environment around the filler and capper machines under a sterile air blanket (“sterile room filling”), or else by maintaining a sterile air blanket around the critical machine sections and their associated ancillaries and conveyors. In principle, this means either maintaining a sterile environment around entire machines, or around the parts of machines where either product or unsealed package is open to its environment.

Maintaining a sterile filling space or a sterile room requires special equipment and operator training (far beyond normal standards in the industry), and involves product risk, because loss of the filling environments sterility is neither quick nor easy to detect.

Aseptic filling of containers is used when filling liquid pharmaceutical compositions onto bottles or bags, filling wines, juices, milk and milk products onto containers such as polymer and paper/cardboard containers prior to distribution to the consumers, or other different products which require a filing under aseptic conditions, i.e., products which are susceptible to decomposition by microbes, such as bacteria, bacilli, fungi, yeasts, or oxidative compounds, or susceptible of being a transferring medium of illnesses, such as transfer of viruses.

What is referred to as aseptic filling of food packages with foods, such as beverages including dairy products, juices, coffee, ice-tea etc, is complicated due to great cleanliness requirements for both package material and filling equipment Normally, a relative risk in the range of one to ten thousand is acceptable, which means that of ten thousand packages that are being filled, at most one package is allowed to be contaminated by, for example, microorganisms.

A known package type and principle for aseptic filling is represented by the system Tetra BrikAseptic@ which is sold by Tetra Pak. In this system, a package material is sterilised by being exposed to H₂O₂ and hot air. This is done when the package material has been formed to a tube and is ready for filling. Before the sterilizing phase, extensive washing with, for instance, acid and lye must be performed.

Aseptic conditions are hitherto generally obtained by using hydrogen peroxide and steam, followed by filling under a blanket of sterile air or nitrogen. Thus pasteurized milk and fruit juices are most often filled into paper/cardboard packages during more or less simultaneous anti-microbial treatment using hydrogen peroxide and steam.

However, the beverage market seeks to attain health, convenience and innovation. In the dairy sector new types of products are introduced all the time. Therefore differentiation of products including packages is most important for a product to survive on the market. As a result aseptic plastic bottles, above all PET bottles, are in increasing demand. PET bottles are gas-tight and easy to open and close and thus satisfy current consumer requirements for health and convenience. If the opening of the bottle is kept constant, the shape and volume of the bottle can easily be varied, which allows differentiation.

U.S. Pat. No. 5,928,607 discloses a method and a device for sterilizing a bottle before filling the bottle with a product. In the described device, UV radiation is used to transform oxygen to ozone at the filling station.

The ozone flows into the bottle and thus sterilises it.

The bottle is then immediately filled with a desired product and sealed. An excimer lamp is used as UV radiation source.

The device disclosed in U.S. Pat. No. 5,928,607 has the advantage that it need not be installed in a sterile clean room. Instead the clean room is reduced to comprise only the interior of the bottle which is sterilised with ozone immediately before filling, so that the bottle is not allowed to be contaminated between sterilisation and filling. A drawback of this device and method is, however, that the ozone can react with the product when the ozone is extracted from the product. Thus the quality of the product may be deteriorated, which for instance may result in the product getting an unpleasant taste. Also remaining ozone residues in the bottle after filling can react with the product and result themselves in a certain unpleasant taste. After a while the ozone residues decompose into oxygen. If the product contains, for instance, fatty acids that turn rancid by oxygen, such ozone residues are devastating to the shelf life of the product.

U.S. Pat. No. 5,342,579 discloses use of an inert nitrogen gas to increase the pressure in the sterilizing agent container in order to propel the sterilizing agent mixture into the sterilization chamber.

Many packages are today made of or contains a major part of polymers, such as so called PET-bottles, paper/cardboard-PET bottles, polymer bags, laminated polymers bags and bottles, laminated polymer-aluminium bags and bottles. These polymer packages are susceptible to heat. Thus PET bottles will deform already at a temperature of 60° C. This means that hydrogen peroxide-steam treatment, which to be efficient is carried out above this temperature, is not a preferred method.

To eliminate this problem it has been proposed to use ozone as a sterilizing agent, as ozone will be active at lower temperatures than will hydrogen peroxide Ozone is an efficient sterilizing agent, as well, and fulfils the requirements of eliminating any hazardous contaminant.

However, when sterilizing packages using ozone, it is of importance that the ozone is being eliminated prior to filling the package, as otherwise the ozone will have a deleterious effect on the product filled into the package, in particular when the product is an organic material, or otherwise of an oxidation sensitive material.

Thus most pharmaceutical compositions in liquid form are sensitive to oxidation by ozone, most food products as liquid or semi-liquid milk and milk products and fruit juices, either as concentrates or in ready-to use concentrations.

WO 2004/087515 discloses i.a., that a step of sterilizing a package further comprises the steps of introducing a sterilizing gas into the package through said passage, and extracting the sterilizing gas by introducing a heavier extraction gas through the passage. This embodiment solves the problem mentioned by way of introduction, i.e. that the sterilizing gas, for instance in the form of ozone, can react with the product if the ozone is extracted from the product Instead the sterilizing gas is extracted by means of another heavier gas, which preferably is inert and thus does not react with the product. A heavier gas can also, both before and after filling of the package with the product, stay in the package and act as a lid preventing pollutants from entering.

Other sterilizing agents are gas compositions of hydrogen peroxide, 1,1,2,2,2-pentafluoroethane (HFC 125), 1,2,2,2-tetrafluoroethane (HFC 134a), or 1-chloro-1,2,2,2-tetrafluoroethane (HGFC 124), 1,1-dichloro-2,2,2-trifluoroethane (HCFC 123), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227 ea), dichlorodifluoromethane (CFC-12), pentafluoro dimethyl ether and ethylene oxide, which possess improved environmental properties as disclosed in U.S. Pat. No. 6,207,109.

The method of extracting the sterilizing gas by a heavier extraction gas, in order to remove, for instance, residues of the reactive sterilizing gas and obtain a protective “gas cover”, can advantageously also be used in sterilisation of a package. A method for sterilisation, filling and sealing of a package may comprise the steps of introducing a sterilizing gas into the package, extracting the sterilizing gas by introducing a heavier extraction gas into the package, filling the package with a product, and sealing the package in a gas-tight manner.

Preferably, the extraction gas is inert. It may contain nitrogen gas, carbon dioxide or some other gas or gas composition, while the sterilizing gas may contain ozone, hydrogen peroxide or some other suitable gas or gas composition. The sterilizing gas is preferably allowed to act for a predetermined time in the package, which time can be, for example, between one and ten seconds for a package volume up to ten litres, i.a., depending on the ozone concentration. It is preferably ensured that both the sterilizing gas and the extraction gas have an overpressure in the package relative to the ambient gas pressure. The opening of the package can advantageously be closed temporarily during sterilisation and filling.

After filling a package with a product, the package is to be sealed. Since also sealing is a technically complicated process, the filled package is usually conveyed to a separate sealing machine which puts a threaded screw stopper or a cap on the package if it is a bottle and applies a top lid by bending or shrinking if the package is a can.

SUMMARY OF THE PRESENT INVENTION

The present invention relates to a method for eliminating gaseous sterilizing agent from a package, in particular oxidation inclined gaseous sterilizing agents, or toxic gaseous sterilizing agents by adding a replacing, displacing or dislocating gaseous material.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In particular the present invention relates to the use of an inert gaseous material to replace a sterilizing agent in gaseous form, wherein the inert gaseous material is selected in such a way that it has a temperature at addition which provides a volume which is smaller than the volume of sterilizing agent to replace at the temperature at which the sterilization takes place, whereby the smaller volume of inert gas expands when the temperature is raising to the temperature of the sterilizing gas.

In accordance with a preferred embodiment of the invention, the density of the gas added at the selected temperature is higher than the density of the gas to be replaced.

In accordance with another preferred embodiment of the invention, the sterilizing agent is ozone.

In accordance with a further preferred embodiment of the invention, the inert gas is nitrogen.

In accordance with another further preferred embodiment of the invention, the nitrogen is added at a temperature below 100 K.

In accordance with another preferred embodiment of the invention, the temperature is 77 K, the nitrogen being in liquid form.

In accordance with a further preferred embodiment of the invention, the sterilizing agent is one or more of hydrogen peroxide, ethylene oxide, pentafluoro dimethylether, 1,1,2,2,2-pentafluoroethane (HFC 125), 1,2,2,2-tetrafluoroethane (HFC 134a), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC 124), 1,1-dichloro-2,2,2-trifluoroethane (HCFC 123), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227 ea), dichlorodifluoromethane (GFC-12).

In accordance with another preferred embodiment of the invention, the sterilizing agent is hydrogen peroxide.

In accordance with another preferred embodiment of the invention, the pressure at filling of inert gas is ambient pressure.

In accordance with another preferred embodiment of the invention, the pressure at filling of inert gas is an overpressure.

In accordance with another preferred embodiment of the invention, the pressure at filling of inert gas is an under pressure or vacuum conditions.

The gas equation reads

$\frac{p_{1} \cdot v_{1}}{T_{1}} = \frac{p_{2} \cdot v_{2}}{T_{2}}$

wherein p is pressure, v is volume and T is temperature (in degrees Kelvin). In an open system p can be neglected, as p₁ is equal to p₂, and thus the ratio v₁ to T₁ is a determinant.

Thus

$v_{2} = {v_{1} \cdot \frac{T_{2}}{T_{1}}}$

This means that if e.g., nitrogen is used at 100 K (−173° C.), one mole of N₂ will take the volume of about 7 litres (22.4 litres at normal pressure and temperature), and when this volume is allowed to warm up, e.g., to 300 K, it will thus expand three times to about 22 litres, thereby displacing any gaseous material present in a substantially closed space. The term “closed space” means here a defined space defining a package, which has an opening to surrounding environment. The term “closed space” has been used to show that most packages are as such relatively well defined and normally has a smaller opening.

By selecting a gas or gas in liquid form having a very low temperature the density of the gas will be such that it, prior to expansion will come underneath any gas having a lower density than the cold gas, and it expansion of the former it will press the “lighter” gas out of the package, even though if the gases should have the same temperature the gas to be expelled is heavier. The method creates an artificially denser gas.

The term package used in the description of the present invention includes vessels, bottles, bags, pouches or boxes; either made of one homogenous material or made of a mixture of materials such as laminated products or products partly consisting of one material, partly of another material.

The materials to be used in the packages thus includes glass, including polymer laminated glass, polymers, such as homopolymers and copolymers, such as PET bottles, homogenous or laminated polymer packages, paper/cardboard packages, combined paper-polymer packages (partly paper, partly polymer), polymer laminated paper, aluminium foil-polymer-paper laminated packages, carton packages, metal sheet packages, such as aluminium packages.

The packages may normally contain anything from some millilitres to a few litres, but may contain even more, such as tenth of litres, hundreds of litres or even thousands of litres.

The content to be filled in the package is normally in liquid state, but can also be semi-liquid, semi-solid, or solid. It may further be in granular, or pulverulent state, or be a solid piece/pieces. The product may even be in gaseous form.

The cool gas is added preferably at the bottom of the package from where the ozone or other sterilizing gas should be expelled. This is done by inserting a tube into the package and allowing the gas to flow into the package. Hereby the volume and temperature of gas added should be such that a sufficient volume expansion is obtained to guarantee a complete replacement of the sterilizing gas.

It may also be advantageous to use double tubes, one for first introducing ozone or other sterilizing gas to fulfil the sterilization requirement, whereupon there is a subsequent addition of nitrogen or other inert gas at a low temperature through the second tube, and thereby using the first tube as an extraction tube for the sterilizing gas.

As ozone is a fairly toxic gas, caution should be observed not to have the ozone gas expelled to the surroundings. Thus the use of an extraction tube, as above, or to use a suction hood over the sterilization station is recommended. The ozone can also be destroyed using chemical catalysts.

The replacing inert gas can as also be added as a liquid. Thus nitrogen can be added in liquid form at a temperature of 77 K (−196° C.) from any dosage equipment for liquids, whereby the nitrogen will fall to the bottom of the package from where it will boil off and form the nitrogen gas expelling the ozone or other sterilizing gas.

Experiments made show that addition of nitrogen at 100 K (−173° C.) in an amount equal to the volume of the bottom will suffice when expelling any ozone present. Further, the experiments show that there is no negative influence on the PET bottles used by the cool gas at the trial.

Another advantage of the invention is that the inert gas, such as nitrogen will form a blanket around or above the package product after having pushed e.g., the ozone away.

A further advantage is that when using an outer container to carry the package to be filled, the outer side of the package to be filled can be treated with a sterilizing gas as well, whereby the inert gas added to the outer container, as well.

If so needed, additional energy can be added to guarantee the expansion of the inert gas or liquid inert gas. Such additional energy can be added via e.g., IR radiation, e.g., by radiate a dark spot on the package with black energy.

It is of importance to sustain non-contamining conditions up to aseptic or sterile filling. One parameter to determine this is by determining the residual flow of inert gas out of the package. The inert gas flow out of the package can be determined in a number of ways to secure this, e.g., by measuring spectral line absorption.

The amount of gas added, either as gas or liquid, should be such that there is a guaranteed outflow of inert gas up to the aseptic or sterile filling machine to avoid any recontamination of the package.

The addition of gas or liquid gas can take place at normal atmospheric pressure, or at an overpressure, or at vacuum conditions. Using normal ambient pressure conditions does not require additional technical apparatus to sustain pressure. Using an overpressure at filling the inert gas will change the balance of the gas equation above, and may allow higher temperature, higher density or better expansion ratios. Using a vacuum condition will provide for i.a., a more rapid filling. 

1. Method for replacing a sterilizing agent in gaseous form with an inert gaseous material in a package to be aseptically or sterile filled, wherein the inert gaseous material is selected in such a way that it has a temperature at addition, which provides volume, which is smaller than the volume of sterilizing agent to replace at the temperature, at which the sterilization takes place, whereby the smaller volume of inert gas expands when the temperature is raising to the temperature of the sterilizing gas.
 2. The method according to claim 1, wherein the density of the gas added at the selected temperature is higher than the density of the gas to be replaced.
 3. The method according to claim 1, wherein the sterilizing agent is ozone.
 4. The method according to claim 1, wherein the inert gas is nitrogen.
 5. The method according to claim 1, wherein the nitrogen is added at a temperature below 100° K.
 6. The method according to claim 5, wherein the temperature is 77° K., the nitrogen being in liquid form.
 7. The method according to claim 1, wherein the sterilizing agent is one or more of hydrogen peroxide, ethylene oxide, pentafluoro dimethylether, 1,1,2,2,2-pentafluoroethane (HFC 125), 1,2,2,2-tetrafluoroethane (HFC 134a), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC 124), 1,1-dichloro-2,2,2-trifluoroethane (HCFC 123), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227 ea), dichlorodifluoromethane (CFC-12).
 8. The method according to claim 1, wherein the sterilizing agent is hydrogen peroxide.
 9. The method according to claim 1, wherein the pressure of the inert gas at filling is ambient pressure.
 10. The method according to claim 1, wherein the pressure of the inert gas at filling is an overpressure.
 11. The method according to claim 1, wherein the pressure of the inert gas at filling is an under pressure or vacuum condition. 